Muffler



March 18, 1941. L. HAAS ETAL MUFFLER 4 Sheets-Sheet 1 Filed Aug. 29, 1959 X/Q ENVENTORS 62; wgafim @kmaw y m.

m w w w wg M I M ATTORNEYS March 18, 1941. L. L. HAAS EI'AL MUFFLER 4 Sheets-Sheet 2 Filed Aug. 29, 1959 "I a AQ INVENTORG ZS 9M BY y I IIIII II In ATTORN EYS Maid! 18, 1 HAAS EIAL MUFFLER 4 Sheets-Sheet 5 Filed Aug. 29, 1959 INVENTORS ATTORNEYS March 18, 1941- L. HAAS ETAL MUFFLER Filed Aug. 29, 1959 Sheets-Sheet 4 Dz 'QI/ZENTQRG ATTORNEYS Patented Mar. 18, 1941 MUFFLER Lucien L. Haas and Gail C. Stark weather, Youngstown, Ohio, asaignors to MacKenzie Muiller Company, Inc., Youngstown, Ohio Application August 29, 1939, Serial No. 292,460

13 Claims.

This invention relates to improvements in muiilers or silencers of the type which are commonly employed for silencing the exhaust of internal combustion engines.

One of the objects ofthis invention is to provide a muiller having a plurality of flow passages of improved construction formed therein. ,An-

other object of this invention is to provide a m mufller of improved construction for providing in which the gases may flow first in one direction and then in another or reverse direction. A further object is to provide an improved reverse flow structure in a muilier which also provides with a shell surrounding the same a silencing chamber. Another object is to provide an improved flow directing member in a muliler which also serves to reinforce against distortion the shell in which the structure is housed.

Another object of this invention is to provide in a muilier a gas flow directing structure which is formed by a pair of sheets having portions thereof secured together and other portions spaced apart to form the flow passages for the 25 gases.

Another object of this invention is to provide a flow directing structure for a muiller formed of a pair of sheets having longitudinal grooved portions formed in each of the sheets, the sheets being secured together so that the grooves of one sheet lie in registration with the grooves of the other sheet to form flow passages for the gases.

Another object is to provide in a flow directing structure of this kind means of improved construction for forming one or more high frequency resonator chambers.

A further object of this invention is to provide a mufller with improved means for forming a bottle neck passage for a resonator chamber.

Other objects of this invention will appear from the following description and claims.

In the accompanying drawings:

45 Fig. 1 is a longitudinal central sectional view of a mufller embodying this invention, the section being taken on line Il, Fig. 2.

Fig. 2 is a transverse sectional elevation thereof, on line 22, Fig. 1.

50 Fig. 3 is a longitudinal central section of a mufller of modified construction, the section being taken on line 3-3, Fig. 4.

Fig. 4 is a transverse sectional elevation thereof, on line 4-4, Fig. 3. i 55 Fig. 5 is a longitudinal central sectional elea portion thereof reverse flow passages through vation on line 55,' Fig. 6, of a muilier of another modified form.

Fig. 6 is a transverse sectional elevation thereof, on line 6-5, Fig. 5.

Fig. 7 is a longitudinal central sectional view, 5 on line l-|, Fig. 8, of still another modified form of muilier embodying this invention.

Fig. 8 is a transverse sectional elevation thereof, on line 8-8, Fig. 7.

Fig. 9 is a fragmentary transverse sectional 1O elevation similar to that shown in Fig. 8 but having two intermediate shells added thereto.

Our improved flow directing structure may be embodied in any suitable or desired type of muf-' iier, and it is understood that our invention is not limited to the particular mufilers shown in the drawings, which merely exemplify certain embodiments of this invention.

The mufllers shown have suitable housings which may, for example, include an outer shell A, which is provided with transverse walls or heads B and C at the opposite ends thereof. In each of the constructions shown, the outer shell A is of elongated or substantially oval or elliptical cross section, but the cross sectional shape of the outer shell may be of any other suitable or desired iorm. While the shell A constitutes the outer shell in each of the constructions shown, yet it will be obvious that, if desired, additional shells may be arranged about the shell A, if desired.

Referring to the particular muffler shown in Figs. 1 and 2, the head B is provided with a suitable aperture through which an inlet duct I5 extends for conducting gases and sound waves from the exhaust pipe of an engine into the interior of a mufller, and the other head C also has an aperture through which a discharge duct I6 extends, to the outer end of which the usual tail pipe (not shown) may be secured.

The mufller shown in Figs. 1 and 2 is of the reverse fiow type and is provided with a structure for directing the flow of gases, which includes a passage or conduit I8 connected with the inlet duct It to receive gases therefrom. The gases discharged from the passage or conduit I8 are reversed, as indicated by the arrow and enter into a second passage or conduit IS, in which they flow toward the inlet head B of the mufiler, whereupon they are again reversed and pass into a conduit or passage 20 which connects with the discharge duct IS. The flow directing structure which includes the passages l8, l9 and 20 may, according to this invention, be formed of a pair of sheets or stampings of metal or other suitable gle piece of sheet material bent over on itself to form two opposed sheets. These sheets .are secured together at portions thereof and} have other portions thereof spaced apart to form the flow passages I8, l9 and 20. Any suitable grooves or depressions may be formed in the sheets or stampings to produce these flow passages and the grooves or depressions may be formed in one or both of the sheets to provide the spaced apart portions thereof. Preferably the flow passages are of approximately cylindrical form, and for this purpose, the two sheets are provided with a series of semi-cylindrical grooves or depressions therein. which, when placed oppositely to each other, form substantially cylindrical passages. For this purpose, one of the sheets is provided with semi-cylindrical grooves or depressions 22, 23 and 24, and the other sheet has similar longitudinal grooves or depressions 25, 26 and 2'! formed therein. The two sheets when placed in proper registration with each other, form the passage 20 by means of the grooves 22 and 25, while the passages I9,

and I8 are formed respectively by the grooves 23, 26 and 24, 21. At their opposite sides, one sheet may be turned over the end of the other sheet to form seams 29 at opposite sides of the sheet and the sheets may also be secured together between grooved portions, for example, by means of welding, as indicated at 30.

In order to complete the flow directing structure, transverse baffles or walls 33 and 36 may be provided at opposite ends of the sheets or stampings. These bailies form chambers 35 and 36 at opposite ends of the flow directing structure and preferably the battles are also provided with flanged portions 36a which may be formed to extend to a slight distance into each of the flow passages 18, I9 and 20 for securing the sheets in fixed relation to the baflies. The bafies may also have flanges on their outer peripheries which may be welded or otherwise secured to the shell A, as indicated at 31. The bafiles, consequently, not only secure the sheets of the flow directing structure in operative relation within the mufiler, but also form walls of the chambers or passages 35 and 36, and furthermore, form between them a chamber within the mufller, which may be used for silencing the noise of the exhaust. In the dividing the chamber between the two baflies into two silencing chambers 38 and 39, see Fig. 2. In order to utilize these chambers for silencing the noise of the exhaust, the groove or depression 22 in one of the sheets or stampings is provided with a. series of apertures or perforations 40 which may extend throughout the length of this groove, and which may vary in number and in cross sectional area according to the particular silencing effect desired. These perforations communicate with the chamber 39, so that parts of the gas pulsations and sound waves may pass into and out of this chamber through the perforations 40. Consequently, this chamber acts as a resonator or silencing chamber in a manner well known in connection with the silencing of engine exhausts. A similar series of apertures 41 are provided in the groove 26 of the other sheet and communicate with the chamber 38, thus producing further silencing of the exhaust. Since the groove 23, in the con- Jnaterial, or if desired, may be formed of a sinstruction shown, is imperforate, gases discharged through the perforations 40 cannot pass into the flow passage l9 and also gases discharged through the perforations 4| cannot pass into the flow passage 20. If desired, however, some apertures may be provided in the groove or depression 2?, so that a portion of the gases may flow through the chamber 39 from the passage 19 directly to the passage 20.

A resonator chamber may also be provided in connection with the flow passage l8, and for this purpose, in the construction illustrated, an intermediate shell 44 is arranged about the grooves 24 and 21 forming the flow passage l8. In the particular construction shown for this purpose, the shell 44 may, for example, be formed by means of a sheet of metal bent into tubular or cylindrical form with flanges 45 extending outwardly therefrom which may be welded to intermediate shell 44. This resonator chamber,'

as will be seen in Fig. 2, is divided by the sheets or stampings into two separate semi-cylindrical parts. A shell of this kind also serves the purposeof preventing exhaust gases and sound waves passing through the perforations from the passage 48 from impinging directly against the outer shell A, which in some cases, causes shell .noises.

Another type of intermediate shell may be employed in connection with any of the flow passages, to provide a high frequency resonator chamber within either of the chambers 38 and 39 and we have by way of example shown such shell 41 in connection with the flow passage 20. This intermediate shell 47 is of approximately semi-cylindrical {01m and has flanges 48 along opposite edges thereof, which may be secured to one of the sheets or' stampings forming the flow passages I8, I53 and 20. For example, one of the flanges 48 of the intermediate shell 41 may be secured to one of these sheets by means of the same welded connections 30 which also connect the two sheets. The other flange 48 of the intermediate shell 41 may be secured in place by the seam 29 connecting a side of each of the two sheets or stampings. When used in connection with an intermediate shell of this type, the groove 25 is perforated to establish communication between the passage 20 and the high frequency resonator chamber within the shell M. It will be obvious that a semi-cylindrical shell of this kind may also be employed in connection with the groove 23 to form another resonator chamber, and if desired, the

intermediate shell 44 may be replaced by two semi-cylindrical shells similar to the shell 41.

In the particular muiiler shown in Fig. 1, a pair of transverse baflles 49 and 50 are provided in the space between the bailie 34 and the end head C. The bafile 49 forms one of the walls of the chamber or passage36 which serves the purpose of conducting gases from the passage I8 into the passage 19, as indicated by the arrow, and this baflie also forms with the bafiie 50 a low frequency resonator chamber 5|. Similarly the baflle 50 forms with the head C a resonator or silencing chamber 52. The baffle 49 may have any suitable or desired aperture connecting the which gases and sound waves may enter the chamber 5| from the chamber or passage 38. This construction also has the advantage that the duct l8 and the baffle 48 are spaced apart so that no rattling can occur because of contact between these parts and this enlarged opening also facilitates the assembly of the mufller. This aperture in the bame 48 may also. if desired, be provided with an annular flange 83 about the discharge duct i8 and spaced therefrom, thus forming an annular passage or bottle neck connecting the reverseflow chamber 38 with the resonator chamber 5|. The baiile 58 may also be provided with an enlarged aperture 54 through which the discharge duct l8 extends, and if desired, additional apertures 55 may be. provided for establishing communication between the chambers 5| and 52.

It is well known that the action of a resonator chamber may be materially modified by the proportions of a bottle neck communicating with the same, and in order to tune the compound resonator chambers 5| and 52 to cancel the desired sound waves, the flange 53 may be made longer or shorter and the aperture enclosed by the flange 53 may also be varied in diameter so that both the cross sectional area and the length of the bottle neck passage formed by the flange 53 in cooperation with the outer surface of the discharge duct I8 may be varied for the proper tuning of the low frequency resonator chambers 8| and 52. The tubular flange 53 is preferably formed integral with the baflle 48 by bending outwardly a portion of the metal which would otherwise be removed to form the hole in the baffle.

In the operation of this muiller, gas pulsations and sound waves entering the muffler through the inlet duct l5 pass into and through the passage l 8, some of the gases and sound waves passing through the apertures in the grooves forming the passage l8 into the chamber formed by the intermediate shell 44 and upon returning from this chamber through the apertures into the passage I8, the returning gas pressure pulsations and sound waves will be out of phase with those in the passage l8, thus producing a silencing and pressure equalizing efl'ect. Fromthe passage |8, the gases enter the chamber 38 and some of the gas pulsations and sound waves entering this chamber will pass through the bottle neck formed by theflange 53 and the'low frequency sound waves returning through the bottle neck to the chamber 38 will in part cancel the pressure pulsations and similar sound waves in the chamber 38, thus further reducing noises and equalizing the flow of gas through the passage l9. In this passage, some of the gas pulsations and sound waves will pass through the apertures or perforations 4| into the chamber 38 and then back into the passage I9. This passage discharges into the flow reversing chamber 35 from which the gases pass into the passage 20. Some of these gases and the sound waves carried thereby will pass out of the perforations 48 into the chamber 39 with a flow equalizing and sound reducing effect similar to that already described in connection with the chamber 38. Some gases and sound waves will pass through the apertures from the passage 28 to the discharge duct l8.

It will be noted that this muflier provides a relatively large number of silencing 'chambers by the use of comparatively few parts, and consequently, a very effective silencing of exhaust gases results from the use of the minimum of material.

In the construction shown in Figs. 3 and 4, the gases enter the muiiier through an inlet duct 88 extending through the head B and pass into a passage 8| formed between a pair of plates 82 and 83, which are grooved, as described in connection with Figs. 1 and '2 to provide the passage 8| and additional passages 84 and 85, the passage being connected with a discharge duct 88. The two grooved sheets 82 and 83 are provided with transverse baffles 81 and 88 at the 0pposite ends thereof, which form with the heads B and C chambers or passages for reversing the flow of gases.

The grooved sheets 82 and 83 extend diametrically across the space within the shell A and form therewith chambers 18 and II, the passage 8| being provided at one side thereof with perforations 12 communicating with the chamber 18, and the passage 84 being provided at the other side thereof with perforations l3, communicating with the chamber II. The silencing action of these chambers upon the gases passing through the passages 8| and 84 is similar to that explained in connection with Figs. 1 and 2. 15 represents an intermediate shell similar to the shell 44 shown in Figs. 1 and 2, except that the intermediate shell 15 is arranged about the passage 85 which communicates with the discharge duct 88.

The flow directing structure embodying this in vention comprising the grooved sheets or stampings secured to each other lends itself particularly to the formation of restrictions in the passages formed by the grooves of the sheets. 8 These restrictions cooperate with surrounding resonator chambers to produce an improved silencing of the exhaust. It is, of course, easily possible to form the grooves in the sheets 82 and 83 so as to provide any desired shape of the passages formed by these grooves. Consequently, we have provided in each of the three passages 8|, 84 and 85 restricted portions 11, those shown preferably having tapering or substantially frusto-conical parts 18 and 18 leading to the restrictions 11. These restrictions operate in the same manner as the restrictions disclosed in our Patents Nos. 2,047,- 442 and 2,047,443. The diameters of the restricted parts 11 may be reduced to any desired extent relatively to the diameters of the passages 8|, 84 and 85 and the restrictions serve to cause a larger flow of gases out of the perforations located ahead of the restrictions, and these gases will flow lengthwise of the resonator chambers 10 and 1| or the resonator chamber formed within the intermediate shell 15, and then back into the conduit or passage through perforations flow passages will be out of phase with those por tions of the gases and sound waves which flow 75 gases and sound waves from the chamber 82 upon straight through these passages, thus resulting in very effective silencing of noises of the exhaust. Restrictions similar to those illustrated in Figs. 2 and 3 may, of course, be used in connection with the mufiler shown in Fig. 1, if desired.

In Figs. and 6 is shown another modified form of mufiler provided with a reverse fiow unit similar to that described in connection with Figs. 3 and 4, this unit comprising a pair of, grooved sheets or stampings 88 and 8| forming passages 82, 83 and 84, the two sheets being arranged between transverse baflles 85 and 86. This arrangement of the reverse flow structure, 'consequently, provides silencing chambers 81 and 88 at opposite sidesof the two sheets. The silencing chamber 81 receives a portion of the gas pulsations and sound waves from the reverse flow passage 84 due to perforations in one wall of this passage, and the chamber 88 similarly receives gas pulsations and sound waves from the middle passage 83. In this construction, an intermediate shell 89 is provided about the passage 82 which receives gases entering the mufller through a duct 98 extending throgh the head B.

In this construction, an additional baflle Si is employed which forms with the batlle 85 a passage or chamber through which gases may flow from one of the longitudinal passages 84 of the reverse fiow structure to the passage 83 thereof. The bafile 9| also forms with the head B a low frequency resonator chamber 92, the baille being provided with an opening or hole 93 throughwhich gas pulsations and sound waves may enter the resonator chamber 92. Preferably the baflle 9| is also provided with an aperture or hole 94 through which the inlet duct 98 extends, and this hole may be made somewhat larger than the external diameter of the inlet duct to provide an an additional opening through which gas pulsations and sound waves may enter the chamber 92 and also to provide ample clearance about the duct 98 to prevent rattling and facilitate assembly of the mufiier.

In the particular construction shown in Figs. 5 and 6, the mufiler is provided at the discharge end thereof with a head C provided with a central aperture through which a discharge duct 95 extends and to which it is secured. The inner end of this duct, consequently, communicates with the middle discharge passage 83 of the reverse flow structure.

In the mufller shown in Figs. 5 and 6, the pas-, sages 82, 83 and 84 are provided with restrictions 97 similar to the restrictions i'i described in connection with Fig. 3, but if desired, these restrictions may be omitted from the reverse flow structure.

In the operation of this mufiler, gases entering the muffler through the duct 98 pass through the passage 82, some of the gases and sound waves passing through the perforated walls thereof into and out of the resonator chamber formed by the intermediate shell 88. The gases and sound waves discharged from the passage 82 enter the space between the bafile 86 and the end head C and pass into the passage 84 of the reverse fiow structure, some of them passing through the perforations of a wall of this passage into and out of the chamber 81, and in passing out of the chamber 84, they enter the space between the battles 85 and SI. Some of the gas pulsations and sound waves will enter the chamber 82, while another portion of the gas pulsations and sound waves enter directly into the passage 83. The

discharging through the aperture 83 entering into the passage 83v will, consequently, be on of phase with gases and sound waves which p directly into the passage 83, thus producing additional silencing of low frequency sound waves and materially reducing the amplitude of the pressure pulsations in the passage 83. From this passage, the gases and sound waves pass through the discharge duct 85 out of the muiiler, some of the gases first paming through the perforations in a wall of the passage 83 into and out of the chamber 88.

In the construction shown in Figs. 7 and 8, the mufller is provided with an inlet head B having a, central aperture through which an inlet duct I88 passes. This duct discharges the gases and sound waves into a central passage I8I formed by means of a pair of grooved sheets or stampings as described in connection with the other figures. The gases and sound waves discharged from the passage IIII enter into a, transverse chamber or passage I82 formed between a baflle I83 of the reverse fiow structure and the end head C of the muiiler, and then enter the passage I84 in which the gases flow in the reverse direction. From the passage I84, the gases enter into a transverse passage or chamber formed between bafiies I85 and I81. From this chamber or passage, the gases enter the discharge passage I88 of the reverse flow structure, and then to the discharge duct I88 of the mufller. The passages I8I, I84 and I88 may be either of approximately cylindrical form, as shown in Fig. 1, or they may be provided with restrictions, as shown in Figs. 3 and 5.

The baflle I85 forms with the inlet head B, a resonator chamber III into which gases may enter through an aperture H2 in the bafile I85. The two sheets or stampings forming the passages I8I, I84 and I88 also divide the space between the two bafiles I83 and I8! into two silencing or resonator chambers H4 and H5, Fig. 8, which cooperate with the passages I8! and I88 respectively in a manner similar to that described in connection with the other figures. The operation of this mufiler is similar to that described in Figs. 5 and 6, and diiiers therefrom mainly in providing for a centrally arranged inlet duct and a discharge duct at one side of the muliler. These various arrangements are necessary to enable the mufilers to be applied to automobiles of different makes, in which the exhaust pipes and tail pipes are so arranged as to require different arrangements of the inlet and discharge ducts of the mumers.

In Fig. 9, we have shown in section a modification of the construction shown in Figs. 7 and 8. In this modification, a pair of substantially semi-cylindrical intermediate shells I28 and I2I are provided, these shells being similar in construction to the shell 41 shown in Fig. 2. Each of the passages IN and I84 is provided with perforations in both of the grooves forming these passages, so that gases and sound waves from the passage I8I may enter into the intermediate chamber formed by the shell I28 as well as into the larger chamber H5. Gases and sound waves from the reverse flow passage I84 enter into the chamber formed by the shell I2I, as well as into the larger chamber II4.

While we have shown in each of the figures, an arrangement according to which the .two sheets or stampings of the reverse fiow structure extend completely across the-chamber in which they are contained, so as to divide the chamber into two separate parts, it will be obvious that. if desired, the enclosing shell A may be made larger, or the sheets, or stampings may be made of smaller dimensions transversely of the muiiler so that they do not extend completely across the space between the transverse baflles of the reverse ilow structure, so that only a single chamber is formed about the sheets or stampings. Such construction may be desired under certain conditions. While we have shown in each of the drawings, a reverse flow structure having three separate passages for ,the gasw, it will be obvious that these sheets may be formed to provide only two passages or more than three passages for the gases and sound waves. It will also be obvious that our improved construction lends itself readily to producing passages of tapering form between the two sheets, it being merely necessary to provide grooves in the two sheets corresponding to the form of passage desired.

The reverse flow construction described in connection with the muillers shown in the drawings has the advantage that the three passages of the reverse flow structure can be simply and inexpensively formed by means of two sheets or stampings suitably shaped to form the passages and secured together. Furthermore, these two sheets in addition to forming the three passages also divide the space between the two transverse baflies of the reverse flow structure into two separate silencing chambers. Consequently, by the use of only four parts, two sheets and two bailles, the three passages for the exhaust gases and two silencing chambers therefor can be formed. Since any or all of the passages of the reverse flow structure can readily be formed so as to receive at either end the inlet and discharge ducts,

it will be obvious that the reverse flow structure may be readily adapted to cooperate with any arrangements of these ducts that may be desired. The reverse flow structure may readily be positioned in any portion of the muiller, so that any desired arrangement of additional silencing chambers may be used in connection with a reverse flow structure.

-By means of intermediate shells which form smaller chambers within the larger chambers of the reverse flow structure, a large variety of silencing efiects can be obtained. The intermediate shells, whether the same are of cylindrical or semi-cylindrical form can be easily applied to the grooved sheets forming the flow passages by means of the same welding or seaming operations employed in forming this flow structure, and consequently, add ,very little to the cost of the muiller.

Our reverse flow structure, while it may be used in connection with an outer or enclosing shell of any suitable or desired form,,has an added advantage when used with a noncircular type of shell such, for example, as shown in the accompanying drawings, in that the reverse flow structure reinforces this shell against distortion. It is well known that, in the event of explosions of gases in the muffler, a shell of elliptical cross section will tend to assume a circular cross section. The reverse flow structure herein disclosed materially reinforces the enclosing shell against such distortion by forming a relatively rigid brace across the major diameter of the elliptical or oval cross section. The muiiler described is also economical to manufacture for the reason that the end heads or transverse partitions B and C in all of the various figures may be identical, but merely differently positioned in the'respective ends of the muiller, so that by diflerent arrangements of the end walls relatively to each other,

and by the provision of an end wall or head havmetal sheets arranged in said chamber and secured together and provided with longitudinal grooves forming between said sheets passages for the gases, said sheets having their opposite sides extending to said shell to divide said chamber into two separated parts, said sheets being provided with perforations in grooved portions thereof establishing communication between said passages and said chamber, said bafiies having openings communicating with said passages.

2. A muiiler having a reverse flow structure formed by a shell, a pair of transverse bailies forming with said shell a chamber, and a pair of metal sheets arranged in said chamber and secured together and provided with longitudinal grooves forming between said sheets passages for the gases, said sheets being secured at their ends to said baiiles and having their opposite sides extending to said shell to divide said chamber into two parts, said sheets being provided with perforations in grooved portions thereof establishing communication between said passages and said chamber, said baiiles having openings communicating with said passages.

3. A muiiler having a reverse flow structure formed by a shell, 8, pair of transverse bafiles forming with said shell a chamber, a pair of metal sheets arranged in said chamber and secured together and provided with longitudinal grooves forming between said sheet passages for the gases, said sheets being secured at their ends to said baiiles and having their opposite sides extending to said shell to divide said chamber into two parts, said sheets being provided with perforations in grooved portions thereof establishing communication between said passages and said chamber, said baiiles having openings communicating with said passages, and means arranged beyond said baflies for conducting gases from one passage to another.

4. A muflier having a reverse flow structure formed by a shell, a pair of transverse baflles forming with said shell a chamber, a pair of metal sheets arranged in said chamber and secured together and provided with longitudinal grooves forming between said sheets passages for the gases, said sheets being secured at their ends to said ballies andhaving their opposite sidesextending to said shell to divide said chamber into two parts, said sheets being provided with perforations in grooved portions thereof establishing communication between said passages and said chamber, said baiiles having openings comsheets arranged lengthwise in said chamber, at l east one of said sheets having longitudinal depressions formed therein which form passages between said sheets, portions of at least one of said sheets forming a wall of a passage having perforations through'which gases may pass into and out of said chamber, said transverse walls having openings connecting with some of said I rations.

passages, some of said longitudinal depressions having transversely extending portions of less depth than the main portions thereof to increase the quantity of gas flowing through said perfo- 6. A muflier having a shell and a pair of walls extending transversely of and connected with said shell and forming therewith a chamber, and means for .conducting gases through said chamber including a pair of metal sheets having portions thereof secured together and other portions thereof grooved to form flow passages between said sheets; -said last mentioned portions of said sheets being provided with perforations through which gases may pass into and out of said chamber, a portion of at least one of said grooves between perforations being of less depth than the main portion thereof to produce a portion of smaller cross sectional area in the passage formed by such groove to cause a larger quantity of gas to flow into and out of said perforations, said transverse walls having openings therein connecting with said flow passages.

7. A muffler having a shell and a pair of walls extending transversely of and connected with said shell and forming therewith a chamber, and means for conducting gases through said chamber including a pair of sheets having portions thereof secured together and other portions thereof grooved lengthwise thereof to form flow passages, said transverse walls having openings therein connecting with said fiow passages, at least one of said sheets having perforations in the portions thereof spaced from the other sheet through which gases may flow into and out of said passages into the space in said chamber,

some of said grooved portions having transverse zones thereof of less depth than the main grooved portions to provide a restriction in a passage to increase the flow of gas through said perforations.

3. A flow directing structure for a muffler comprising a shell, a pair of transverse walls secured to said shell, and a pair of sheets extending from one of said walls to the other end having its sides terminating at said shell and having portions thereof spaced from said shell to form with said shell a pair of chambers, parts of said sheets being secured together and other portions thereof being spaced apart to form flow passages between said sheets, said walls having apertures communicating with said passages, a portion of one of said sheets forming a wallof one of said passages having perforations communicating with one of said chambers for permitting gases to flow therethrough into and out of said chamber, and a portion of said other shell forming a wall of another passage having perforations communicating with the other of said chambers for perm'iting gases from said last mentioned passage to flow into and out of said last mentioned chamber. I

9. A mufller having a flow structure-formed by a shell, a pair of transverse walls forming a chamber with said shell, a pair of metal sheets arranged between said walls and secured together, at least one of said sheets having grooves,

formed lengthwise therein which form between said sheets passages for the gases, means for conducting gases to and from said structure into said passages, and an intermediate half shell arranged in said chamber about a part of a passage and having its longitudinal edges secured to one of said sheets, a wall of said passage having perforations through which gases may pass into and out of the space within said intermediate shell.

10. A flow directing structure for a mufller comprising a shell, a pair of transverse walls secured to said shell, and a pair of metal sheets extending from one of said walls to the other end having its sides terminating at said shell and having portions thereof spaced from said shell to form with said shell a pair of chambers, parts of said sheets being seemed together and other portions thereof being spaced apart to form flow passages between said sheets, said walls having apertures communicating with said passages, a portion of one of said sheets forming a wall of one of said passages having perforations communicating with one of said chambers for permitting gases to flow therethrough into and out of said chamber, a portion of said other sheet forming a wall of another passage having perforations communicating with the other of said chambers for permitting gases from said last mentioned passage to flow into and out of said last mentioned chamber, and an intermediate shell arranged within said first mentioned shell about a third passage formed by said sheets and forming therewith a silencing chamber, portions of said sheets forming said third passage being perforated to permit gases to pass into and out of the space within said intermediate shell.

11. A muffler having a flow structure formed by a shell, a pair of transverse walls forming a chamber with said shell, a pair of sheets arranged between said walls and secured together,

at least one of said sheets having grooves formedlengthwise therein which form between said sheets passages for the gases, means for conducting gases to and from said structure into said passages, and a substantially semi-cylindrical shell secured to one of said sheets about a portion thereof forming a wall of a passage and forming with said sheet a silencing chamber, said portion of a sheet having perforations communicating with said chamber.

12. A mumler having a reverse flow ,structure formed by a shell, a pair of transverse bafiles forming with said shell a chamber, and a pair of sheets arranged in said chamber and secured together and provided with longitudinal grooves forming between said sheets passages for the gases, said sheets having their opposite sides extending to said shell to divide said chamber into two separated parts, said sheets being provided with perforations in grooved portions thereof establishing communication between said passages and said chamber, the perforations of one passage communicating with one part of said chamber and the perforations of another passage communicating with the other part of said chamber, and means for conducting gases to flow in succession from one of said passages to another.

. 13. A mufller having a flow structure formed by a shell, a pair of transverse walls forming a chamber with said shell, a pair of metal sheets arranged between said walls and secured together, at least one of said sheets having grooves formed lengthwise therein which form between said sheets passages for the gases, means for conducting gases to and from said structure into said passages, and a substantially cylindrical longitudinally split intermediate shell extending about a longitudinal edge of said sheets and about a groove adjacent to said edge and having its longitudinal edges at said split secured to said sheets,

at least one of said sheets at said groove having perforations through which gases may pass into and out of the space between said intermediate shell and said sheets. I

LUCIEN L. HAAS.

GAIL C. STARKWEATHER. 

